|Subject:||Re: LF: Finbar's Compact 500kHz Vertical|
|From:||Rik Strobbe <[email protected]>|
|Date:||Wed, 18 Jun 2008 10:34:59 +0200|
|References:||<[email protected]> <[email protected]> <[email protected]> <[email protected]>|
I can not find any reason to believe that the same ERP radiated from 2 antennas with the same radiation pattern could produce different field strengths.
But I am far from an antenna specialist or propagation specialist, so maybe others can come up with these reasons.
At the moment we talk about skywave (ionospheric) propagation there might be no such thing as "the best antenna". An antenna that has a high takeoff angle may be superior to an antenna with a low takeoff angle at shorter distances (let's say less than 1000...1500km) while the low angle antenna will do better at long distances.
http://www.seefunk-fx-intern.de/radiobeacon/radiobeacon_en.htm provides some figures:
- The TX has 18W input, at 75% efficiency this means about 13 W output.
- The antenna current is +/- 1.7 A, assuming 13W output the total resistance (Rrad + Rloss) is only 5 Ohm.
- The antenna top is 35m asl. Based on the picture I estimate that the antenna bottom is +/- 10m asl, so antenna hight is +/- 25m. The topload seems about twice as long as the antenna height so let's estimate 50m. According to "mmana-ga"l Rrad is 2.3 Ohm, the antenna capacitance is 840pF (the website notes +/- 800pF, so thta's pretty close) and the gain is 4.64dBi (2.5dBd).
- Putting 1.7A into 2.3 Ohm means 6.65 Watt radiated or +/- 12 Watt ERP.
No wonder they are putting out such strong signal.
73, Rik ON7YD - OR7T
At 00:51 18/06/2008, you wrote:
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